1. Field of the Invention
The invention relates to an inkjet printhead applicable to an image forming apparatus which records information or others on a recording medium by ejecting ink droplets from a plurality of nozzles.
2. Description of Related Art
There is known an inkjet printhead including a cavity unit and a piezoelectric actuator laminated on the cavity unit. In the cavity unit are formed a plurality of ink passages each constituted by a common ink chamber, a pressure chamber, a connecting passage that connects the common ink chamber with the pressure chamber, and a nozzle in communication with the pressure chamber, such that ink as supplied from an ink supply source into the common ink chamber is distributed to a plurality of the pressure chambers via a plurality of the connecting passages and then flows to the nozzles, along the ink passages. By selectively applying a pressure to the ink in a pressure chamber by driving the piezoelectric actuator, a droplet of the ink is ejected from a nozzle corresponding to the pressurized ink chamber.
For instance, in cavity units disclosed in JP-A-2004-223880 (see FIGS. 3 to 5) and JP-A-2004-160874 (see FIG. 3), an ink passage is formed by laminating a plurality of plates in which recesses and/or through-holes are formed, such as a plate where nozzles are formed, a plate where pressure chambers are formed, a plate where common ink chambers are formed, and a plate where connecting passages that connect the pressure chambers with the respectively corresponding common ink chambers.
In the cavity units of the above-mentioned publications, the connecting passage between each pressure chamber and the common ink chamber includes an orifice portion for restricting flow of the ink so that the pressure applied to the pressure chamber is efficiently transmitted to the nozzle. That is, the orifice portion damps out a pressure wave coming from the pressurized pressure chamber to the common ink chamber. In the first publication, i.e., JP-A-2004-223880, such orifice portions are formed in a first one of two plates sandwiched between the plate in which the common ink chambers are formed and the plate in which the pressure chambers are formed, which first plate is on the side of the plate in which the common ink chambers are formed. In the second publication, i.e., JP-A-2004-160874, the orifice portions are formed in the plate in which the pressure chambers are formed, such that the orifice portions are continuous from the pressure chambers.
More specifically, in the first publication, each orifice portion takes the form of a groove having a depth D and extending along a major surface of the first plate, and an end of the groove is connected to a through-hole formed through the first plate while the other end of the groove constitutes a terminal portion communicated with the pressure chamber. That is, the orifice portion extends between the through-hole and the terminal portion, and a width of the orifice portion, which is a dimension thereof in a direction perpendicular to a direction of flow of the ink, is W1 that is smaller than a width or a dimension W2 of the through-hole in the same direction and a width or a dimension W3 of the terminal portion in the same direction. Thus, a cross-sectional area of the connecting passage is reduced at the orifice portion so as to increase a resistance to the ink flow there.
In the second publication, the orifice portion takes the form of a groove formed to have a depth D in a major surface of the plate, similarly to the orifice portion in the first publication. An end of the orifice portion is directly connected with a pressure chamber formed through the thickness of the plate, and the other end of the orifice portion constitutes a terminal portion communicated with the common ink chamber. This orifice portion is also between a through-hole in the form of the pressure chamber and the terminal portion, and a width of the orifice portion or a dimension thereof in a direction perpendicular to the ink flow is W1 that is smaller than that W2 of the pressure chamber and that W3 of the terminal portion, thereby reducing a cross-sectional area of the connecting passage at the orifice portion to increase a resistance to the ink flow there.
Orifice portions such as those disclosed in the first and second publications are typically formed in a metal plate by wet etching. Where the through-holes or the pressure chambers and the grooves (i.e., the orifice portions and terminal portions) are continuously formed in a same plate, as described above, it is typical that the through-holes or the pressure chambers are first formed through the plate, and then the orifice portions are formed by “half etching”, that is, by etching away the material of the plate halfway in a direction of its thickness. The wet etching is performed such that an etchant is flowed on one surface of the plate in which the grooves are open, with each part not to be etched in both of opposite surfaces of the plate being covered with a protective film.
When the orifice portions are formed by half etching, the through-holes or the pressure chambers are already formed. Hence, around the through-holes or the pressure chambers, the etchant tends to flow more rapidly and a speed at which the etching process proceeds is accordingly higher at this place than at the other places. In addition, at a boundary between the through-hole or the pressure chamber and the orifice portion in each connecting passage, the width of an ink passage or the connecting passage decreases from W2 to W1 as well as the depth decreases from the entire thickness of the plate down to D, and an edge portion protruding inward is formed. Since at this boundary the etching speed is high and the etching process is excessively promoted, the edge portion is etched away so that the width W1 and the depth D at a part of the orifice portion on the side of the through-hole or the pressure chamber become larger than their design values. Thus, a problem is caused that although the resistance of the orifice portion to the ink flow is regulated by suitably determining the cross-sectional area of the orifice portion, the finished orifice portion does not have dimensions precisely as designed.